linux-kernel - Re: [tip:perf/urgent] perf/x86: Enable raw event access to Intel offcore events

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Message-ID: <1321912084.28118.38.camel@twins>
Date:	Mon, 21 Nov 2011 22:48:04 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Vince Weaver <vweaver1@...s.utk.edu>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	mingo@...e.hu
Subject: Re: [tip:perf/urgent] perf/x86: Enable raw event access to Intel
 offcore events

On Mon, 2011-11-21 at 22:45 +0100, Stephane Eranian wrote:
> On Mon, Nov 21, 2011 at 10:42 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Mon, 2011-11-21 at 22:39 +0100, Stephane Eranian wrote:
> >> To solve this problem (in the general case), you need to know which
> >> counter is taken (or required)
> >> by ALL pinned system-wide events across all CPUs. Once you've
> >> constructed the bitmap, you can
> >> use it as the basis (used_mask) to try and schedule the group events.
> >>
> > Its worse, you also need to consider all task-pinned events if you want
> > to be complete. That's an even worse problem.
> >
> But that you know because by the time you do the simulation you already
> know the task the events are attached to. You can get to the list of events
> already attached to the task. Again this is a best effort, it could well be
> that someone else attaches pinned task events just after the simulation.

In the PAPI case yes, but what if you want to create a CPU-wide group,
then you need to consider all task-pinned events that could possibly
land on your CPU. Not fun.


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